Antiglare coating and articles

ABSTRACT

The present invention relates to articles comprising an antiglare layer, coating compositions suitable for making antiglare layers, methods of making an antiglare article, and methods of making antiglare coating compositions. In some embodiments the article is a (e.g. illuminated) display article such as a touch screen. The antiglare layer comprises aggregate inorganic oxide particles in a cured inorganic polymer matrix.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/926,722,filed Aug. 26, 2004, now U.S. Pat. No. 7,294,405.

BACKGROUND

As described in U.S. Pat. No. 5,725,957, there are primarily two methodsof reducing glare associated with surfaces of glass substrates. Thefirst method involves depositing an “interference” coating stack on theglass substrate that controls glare by taking advantage of the opticalinterference within thin films. Such films usually have a thickness ofabout one-quarter or one-half the nominal wavelength of visible light,depending on the relative indexes of refraction of the coating andglass. The second method involves forming a light scattering, i.e.diffusing, means at the surface of the glass, usually either by alteringthe characteristics of the outermost surface of the glass substrate orvia a diffuser coating on the glass substrate.

Interference coatings reduce glare without reducing resolution. However,they are relatively expensive to deposit, requiring the use ofrelatively high cost vacuum deposition techniques such as sputtering andprecise manufacturing conditions, or very precise alkoxide solution dipcoating techniques, with subsequent drying and firing. Strict thicknesscontrol and uniformity are required.

In attempting to reduce glare by diffusion of light, one approach hasbeen to etch the outer surface of the glass substrate, or otherwisemodify the outer surface of a coating deposited on the glass substrate.There are numerous drawbacks in etching or otherwise modifying thesurface characteristics of a substrate or coated substrate. Etching bychemical means involves handling and storage of generally highlycorrosive compounds (e.g. hydrofluoric acid). Such compounds createprocessing and disposal problems in view of increasingly stringentenvironmental laws. Etching by non-chemical means, such as bysandblasting, necessitates additional and costly processing operations.In U.S. Pat. No. 5,725,957, a transparent substrate is spray coated witha precursor solution formed by dissolving a precursor of an inorganicmetal oxide in an organic solvent. As an alternative, another approachhas been to incorporate diverse materials (e.g. mixed oxides havingdifferent refractive indexes) into coating compositions.

Although various approaches of reducing glare have been described,industry would find advantage in new approaches for providing anantiglare surface.

SUMMARY OF THE INVENTION

In one aspect the invention relates to an article such as a touch screencomprising a glass substrate, an active element for detecting a touch onthe touch screen, and an antiglare layer. The antiglare layer comprisesaggregate inorganic oxide particles in a cured inorganic polymer matrixwherein the aggregates form surface structures ranging in size fromgreater than 2 micrometers to about 100 micrometers. The active elementmay comprise a transparent conductive layer (e.g. comprised oftransparent conductive oxide) disposed between the glass substrate andthe antiglare layer.

In some embodiments, the (e.g. touch screen) article preferablycomprises a silicon oxide layer disposed between the transparentconductive layer and the antiglare layer and/or a liquid crystal silanesurface layer.

The (e.g. touch screen) article typically has any one or combination ofthe following optical properties including a reflected haze of at least150, a reflectance of less than 10%, and a transmission of at least 80%.

The (e.g. touch screen) article typically has any one or combination ofthe following durability properties including a scratch resistance asdetermined by the Nanoscratch Test of at least 10 mN, a Taber AbrasionResistance test of at least 100 cycles, and a time to failure asdetermined by the Polishing Test of at least 2 hours for a 1 micrometerantiglare layer.

The inorganic oxide particles typically have a mean particle sizeranging from about 0.05 micrometers to about 0.15 micrometers.

The surface structures typically have a dimension of at least 10micrometers or 20 micrometers. The surface layer has a total surfacearea and the surface structures comprise at least 20%, at least 30% orat least 40% of the total surface area.

The cured inorganic polymer matrix is typically derived from anorganosilane such as a silicon alkoxide. The cured organosilane istypically derived from a sol-gel process.

In other embodiments, the invention relates to a coating compositioncomprising an organosilane and flocculated inorganic oxide particlesranging in size from greater than 2 micrometers to about 100micrometers. The inorganic oxide particles are typically present in aconcentration of less than 1.5 wt-%.

In another embodiment, the invention relates to a method of making anantiglare article with the coating composition.

In another embodiment, the invention relates to a method of making anantiglare coating composition comprising providing an inorganic polymerprecursor and colloidal silica particles having a mean particle sizeranging from 0.05 micrometers to 0.15 micrometers; and forming aninorganic polymer solution concurrently with flocculating colloidalsilica aggregates having a mean particle size of greater than 2micrometers.

In another embodiment, the invention relates to a (e.g. touch screen)article comprising an antiglare layer having a synergistic balance ofoptical properties and durability. The article preferably has atransmitted haze of less than 30% (e.g. less than 20%, 10% or 5%),transmission of at least 80% (e.g. at least 85% or 90%), clarity of atleast 70% (e.g. 80%), and a scratch resistance as determined by theNanoscratch Test of at least 10 mN.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three dimensional view of a touch panel having an antiglaresurface layer in accordance with the invention.

FIG. 2 depicts the particle size distribution of an illustrativecolloidal inorganic oxide suitable to be employed for making anantiglare surface layer.

FIG. 3 is an illustrative antiglare surface at a magnification of 50×.

FIG. 4 depicts the particle size distribution of another illustrativecoating composition employed for making the antiglare surface.

FIG. 5 is another illustrative antiglare surface at a magnification of50×.

FIG. 6 is another illustrative antiglare surface at a magnification of20×.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to articles comprising an antiglare (e.g.surface) layer, coating compositions suitable for making antiglarelayers, methods of making an antiglare article, and methods of makingantiglare coating compositions. In some embodiments the article is a(e.g. illuminated) display article such as a touch screen.

Various touch screens are known in the art, such as those described inU.S. Pat. Nos., 4,198,539; 4,293,734; and 4,371,746; incorporated hereinby reference. Touch screens typically comprise a (e.g. computer) touchsensitive panel such as commercially available from 3M Touch Systems,Inc., Methuen, Mass.

One exemplary display 10 of FIG. 1 includes touch panel 12 that includesan insulative substrate 14, such as glass, plastic or anothertransparent medium and active portion 15 on substrate 14. Active element15 for detecting a touch input typically includes a transparentconductive layer 16 deposited directly on substrate 14. Layer 16 istypically a doped tin oxide layer having a thickness of twenty to sixtynanometers and may be deposited by sputtering, vacuum deposition andother techniques known in the art. Conductive layer 16 may also includea conductive polymeric material or a conductive organic-inorganiccomposite. A conductive pattern, (not shown), is typically disposedabout the perimeter of conductive layer 16 to provide a uniform electricfield throughout conductive layer 16 in order to establish the point ofcontact between the display and a finger or stylus. Second conductivelayer 20 may optionally be provided to shield display 10 from noise thatmay result from the electric circuits of a display unit, (not shown), towhich display 10 may be attached and may similarly include a tin oxidelayer deposited in a similar manner as discussed with reference toconductive layer 16. The touch panel includes an antiglare layer 18 inaccordance with the invention.

In the article of the invention the antiglare layer may be present as asurface layer, such as depicted in FIG. 1. Alternatively, the antiglarelayer is disposed between the surface layer and the substrate. Thepresence of layers above the antiglare layer does not detract from thestructural features, the optical properties, nor the durabilityproperties of the antiglare layer as will subsequently be described.

The antiglare surface layer comprises aggregate inorganic oxideparticles in a cured inorganic polymer matrix. The aggregate inorganicoxide particles have a maximum dimension ranging in size from 0. 1micrometers to about 100 micrometers. The aggregate inorganic oxideparticles preferably have a maximum dimension of at least 0.2micrometers and more preferably at least 0.3 micrometers. The discreteinorganic oxide particles that form the aggregates are substantiallysmaller in size than the surface structures. As used herein, an“aggregate” refers to at least two particles bonded together. Thesurface structures are comprised of one or more aggregate inorganicoxide particles. Accordingly, the surface structures have a maximumdimension of at least the size of a single aggregate.

Without intending to be bound by theory, by use of a cured inorganicpolymer matrix to bind the surface structures, the resulting antiglaresurface can advantageously provide a synergistic balance of antiglareoptical properties in combination with high levels of durability.Antiglare is typically characterized by a combination of opticalproperties. Among such optical properties, reflected haze andreflectance are usually most indicative of the antiglare property. Theantiglare surface layer described herein generally has a reflectance ofless than 10%. The reflected haze is typically at least 150 and moretypically at least 200. The reflected haze is usually less than 600 andmore typically less than 550. However, the application of an antiglarecoating can reduce the transmission, transmitted haze, and clarity. Thetransmission is generally greater than 80%. Preferably, the transmissionis at least 85% and more preferably at least 90% or greater. Thetransmitted haze of the antiglare surface layer is typically less than30% and preferably less than 25%. Antiglare surface layers havingrelatively small surface structures can provide a transmitted haze ofabout 10%, whereas antiglare surface layers having larger surfacestructures can provide transmitted haze values of less than 10%. Forexample, the transmitted haze may be less than 8%, 7% or 6%. The clarityis at least 70% and preferably at least 80%. The test methods fordetermining such optical properties are described in the forthcomingexamples.

In combination with the optical properties just described, the antiglaresurface layer also exhibits high levels of durability. For example, thetouch screen has a scratch resistance as determined by the NanoscratchTest of at least 10 mN and preferably of at least 30 mN. Alternativelyor in addition thereto, the touch screen has a time to failure asdetermined by the Polishing Test of at least 2 hours for a 1 micrometerantiglare layer. Alternatively or in addition thereto, the touch screenhas Taber Abrasion Resistance of at least 100 cycles with CS-10Fabrasive wheels and a load of 500 g. The test methods for determiningsuch durability properties are described in the forthcoming examples.

A variety of colloidal inorganic oxide particles may be employed in theantiglare layer described herein. Suitable inorganic oxides include forexample silica, ceria, alumina, zirconia, titania, and mixtures thereof.Silica is a preferred inorganic oxide particle, particularly when usedin combination with an organosilane based inorganic polymer matrix.

As depicted in FIG. 2, typically, about 95% by weight of the colloidalinorganic oxide particles employed to form the aggregates range in sizefrom 0.005 micrometers to 0.30 micrometers. The starting colloidalinorganic oxide particle distribution may be substantially free ofparticles having a particle size in excess of 0.30 micrometers. Thestarting colloidal particles may be substantially larger as well, forexample the starting colloidal inorganic oxide particles may have a meanparticle size ranging from about 0.005 micrometers to 0.5 micrometers.

The Applicant has found that relatively large aggregates can be formedfrom colloidal (e.g. silica) inorganic oxide having a mean particle sizeof about 0.15 micrometers (150 nm). In order to obtain such relativelylarge aggregates, substantially all of the starting colloidal particlesmay be flocculated into aggregates, as depicted in FIG. 4. The size ofthe resulting aggregates may range from 0.30 micrometers (e.g. twice themean particle size of the starting colloidal inorganic oxide particles)to 100 micrometers (i.e. 1000 times the mean particle size of thestarting colloidal inorganic oxide particles). It is typically preferredthat the aggregate particles have a mean size of at least 2 micrometersand preferably a mean size of less than 40 micrometers. Typically, thesize of the aggregates is somewhat evenly distributed throughout theaggregate size range.

An exemplary antiglare surface layer, at a magnification of 50× and 20×,that was prepared from a coating comprising relatively large aggregates,is depicted in FIGS. 5 and 6 respectively. There is a combination oflarge surface structures (100) and comparatively smaller surfacestructures (200) typically surrounding the large surface structures.These structures are anchored by the cured inorganic polymer matrix.Relatively large surface structures can be advantageous for providinglow levels of haze (i.e. 5% or less).

The average maximum dimension of the large structures is typically atleast 10 micrometers. Further, the average maximum dimension of thelarge structures is typically less than 50 micrometers (e.g. less than40 micrometers). The average size of the large structures, such asdepicted in FIG. 6 is 25 micrometers. Further, 95% of the surfacestructures of FIG. 6 have a maximum dimension of less than 70micrometers. The aspect ratio of these surface structures is at leastabout 1:1 and typically no more than about 5:1 and the structures aregenerally irregular in shape. The irregularity of these surfacestructures may be beneficial to the overall antiglare properties of thesurface.

The individual large structures may have a single peak, the peak rangingin size from a single aggregate inorganic oxide particle (e.g. about0.15 micrometers) to about 10 micrometers. It is common for suchindividual large structures to be generally shaped like a cone with thebase anchored on the substrate by the inorganic polymer. Accordingly,there is a decreasing gradient of particles and/or particle aggregatesspanning from the apex of the cone to the peripheral edges of the baseof the cone. As depicted in FIG. 5, it is not uncommon for a singlesurface structure to comprise multiple neighboring peaks. For example,each surface structure may have two to ten distinct peaks. Each distinctpeak may be greater than about 4 micrometers and may contain a number ofaggregates less than 4 micrometers in size.

The individual large surface structures may be separated from thenearest large surface structures by a distance ranging from about 2micrometers to about 50 micrometers. The majority of large surfacestructures are separated by a distance of about 15 micrometers onaverage.

As would be appreciated by one of ordinary skill in the art, theantiglare surface may comprise various combinations of relatively smallinorganic oxide surface structures in combination with relatively largeinorganic oxide surface structures. The surface area of the surfacestructures relative to the total surface area of the antiglare layer istypically at least about 20%. The surface area of the surface structuresis typically no greater than about 60%. In at least some embodimentsthat provide low levels of haze, the surface area of the surfacestructures range from about 25% to 35% of the total surface area of theantiglare layer. In other embodiments, such as antiglare surface layersformed from relatively small inorganic oxide aggregates, the surfacearea of the surface structures ranges from about 40% to about 50%.

In some embodiments, such as in the case of relatively small surfacestructure regions as exemplified in FIG. 3, the surface structures areapproximately evenly distributed. Hence the distance between surfacestructures, i.e. unstructured land portions (300) of the surface, hasabout the same dimensions as the size of the structures. In otherembodiments, such as in the case of larger surface structures asexemplified in FIGS. 5 and 6, the surface area of the unstructured landportions between surface structures may be considerably larger.

The inorganic polymer preferably includes a source of silica that whensufficiently heated forms SiO₂.

The cured inorganic polymer matrix is preferably an organosilanesolution cured by means of heat. Organosilane solutions are known in theart and are typically derived from a “sol-gel” process.

Organosilanes can be represented by the following general formulaR_(n)SiX_(m)  (Formula I)

wherein R is an organofunctional group bounded to the silicon atom; X isa hydrolyzable group, such as a halogen or an alkoxy group, attached tothe silicon atom; n is 1 or 2; and m is 4-n.

A preferred organosilane solution is synthesized from the hydrolysis andcondensation of silicon alkoxides. (See for example C. J. Brinker and G.W. Scherer, “Sol-Gel Science”, Academic Press, 1990.) Such silanes havea molecular structure that is highly ordered. Preferred siliconalkoxides include for example tetraethoxysilane, methyltriethoxysilane,and mixtures thereof. Other suitable organosilanes are known in the art,such as described in EP 1 077 236.

A medium is typically used to dilute the organosilane as well as totransport the silane to the surface of the substrate being coated.Additionally, water reacts with organosilanes to form hydrolyzedproducts or silanols. Hydrolysis reactions between water andorganosilanes can be catalyzed in an acidic solution. Thus, astabilizing agent may be used so that the silanols are stable againstself-condensation reactions that may cause precipitation of the solutionif the solution is basic. The bond formed between the silanol and thesubstrate is accomplished through a cross condensation reaction. Thecross condensation reaction between a silanol and a molecule on thesubstrate is generally slow. This reaction can be accelerated byheating.

The antiglare surface layer is typically prepared from analcohol-containing coating composition. The aggregates can be formed byflocculating colloidal (e.g. silica) inorganic oxide from a colloidal(e.g. silica) inorganic oxide precursor dispersed in an organosilanesolution. Accordingly, the flocculated particles are preparedconcurrently with the preparation of the organosilane solution.Alternatively, however, the aggregates can be separately formed,optionally separated from the non-flocculated particles, and then addedto a stable organosilane solution.

The method of preparing the antiglare coating generally involvespreparing an organosilane solution (e.g. via sol-gel processes)including (e.g. silica) inorganic oxide particle precursor anddestabilizing the composition in order to flocculate at least a portionof the inorganic oxide particles. Various methods of flocculatingcolloidal (e.g. silica) inorganic oxide particles are known such asdescribed in “One step antiglare sol-gel coatings for screens by sol-geltechniques”, Journal of Non-crystalline Solids 218 (1997) 163-168 andU.S. Pat. No. 5,998,013.

A preferred method of flocculation includes reacting colloidal (e.g.silica) inorganic oxide with at least one of several silicon alkoxideprecursors to form a silane precursor and destabilizing the solution byaddition of acid. A variety of acids can usefully be employed. Typicallyinorganic acids such as hydrochloric acid, nitric acid, and the like areutilized. The solution may further comprise an adhesion promoter,sintering aid or flux to improve coating densification during the curingstep. Sodium acetate is a suitable additive. In the preparation thereof,the order of addition of these materials can vary. For example, thesilicon alkoxide precursors can be dispersed in an alcohol solution,followed by (e.g. sequential) addition of the sintering aid and acid.This mixture can then be combined with the colloidal (e.g.silica)inorganic oxide solution. This order of addition is preferred forobtaining relatively large aggregates. Alternatively, the siliconalkoxide precursors can first be combined with the colloidal (e.g.silica) inorganic oxide solution, followed by the (e.g. sequential)addition of the acid, sintering aid, and alcohol.

In greater detail, an antiglare coating composition can be prepared bycontinuously stirring tetraethoxysiliane and methyltriethoxysilane with100 nm colloidal silica in ethylene glycol. While stirring, a diluteacid/sodium acetate trihydrate mixture is added to destabilize theparticle precursors and initiate flocculation particle growth of theparticle precursor. The dilute acid also initiates and sustainshydrolysis and condensation reactions of the silicon alkoxide precursorsby providing both the water of hydration and the acid catalyst. Afterthe reaction is complete, a partially hydrolyzed ethyl silicate sol isyielded containing metastable silica floccules of about 0.5-150 μm.Alcohol diluents of 1-butanol and 2-propanol are then added to furtherstabilize the coating composition and adjust the viscosity as requiredfor application. This method produces relatively large aggregates aspreviously described.

The (e.g.silica) inorganic oxide aggregates are formed from uniformlydispersed colloidal (e.g.silica) inorganic oxide in a hydrophilicsolvent such as an alcohol. Examples of suitable solvents include1-butanol, 2-propanol, ethanol, ethyl acetate, ethylene glycol,propylene glycol, acetone, and the like. The solvent may be used singlyor as a combination of two or more types. The percent solids in thecolloidal (e.g. silica) inorganic oxide dispersion is generally about5-50% (preferably, about 15-30%), based on the total weight of thecolloidal (e.g. silica) inorganic oxide dispersion. Colloidal silica iscommercially available from various suppliers. Nyacol Nanotechnolgies,Inc. Ashland, M A and Alfa Aesar, Ward Hill, M A both supply alcoholbased sols having a mean particle size ranging from 20 to 50 nm. Onepreferred colloidal silica is a 30% solution of 100 nm colloidal silicain ethylene glycol, commercially available from Nanotechnologies, Inc.under the trade designation “Nyacol DP5540”.

Typically, small concentrations of colloidal (e.g. silica) inorganicoxide are employed. Preferably the concentration of colloidal (e.g.silica) inorganic oxide is less than 5 wt-% of the coating composition.More typically, the concentration of colloidal (e.g.silica) inorganicoxide is less than 4 wt-% and more preferably less than 3 wt-%. TheApplicant has found that good antiglare properties can be obtained withcoating compositions comprising less than 2 wt-% colloidal (e.g. silica)inorganic oxide. For this embodiment, it is preferred to employcolloidal (e.g. silics) inorganic oxide at concentration of 1.5 wt-% orless and even 1.0 wt-% and less. Relatively large surface structures,such as depicted in FIG. 5, can be obtained with less than 0.5%.Typically the concentration of colloidal silica in the coatingcompositions is at least 0.05%.

The coating compositions are generally stored in a closed container withstirring at room temperature for about 2 to 10 days prior to employingthe coating composition to coat a substrate. The aggregate-containingorganosilane coating solution is applied with a suitable method thatyields a thin substantially uniform layer. Precision dip coatingmachines are a preferred means of coating due to their smooth motion atprecise and accurate withdrawal speeds. When appropriately modified tothe proper rheology, the coating compositions described herein can beapplied by spray coating, meniscus coating, flow coating, screenprinting, or roll coating.

The coating compositions described herein exhibit sufficient adhesion toa wide variety of substrates. Glass and (e.g. ceramic) materials arepreferred substrates for illuminated display panel due to being bothtransparent and highly durable. The thickness of the glass substratetypically ranges from about 0.4 mm to about 4 mm. Soda lime glass andborosilicate glass are typically used for displays. The presentinvention is also suitable for improving the durability of antiglarecoatings on various plastic substrates, such as polycarbonate,polymethylmethacrylate, or cellulose acetate butyrate.

Alternatively, the transparent substrate may be a plastic film. Thethickness of the transparent substrate is generally at least 20micrometers and often at least 50 micrometers. Further, the transparentsubstrate is often less than 500 micrometers, and more often less than250 micrometers. The surface of the plastic film may be treated, wheredesirable, to increase adhesion of the antiglare layer. Examples of sucha treatment include formation of roughness on the surface by sandblasting or with a solvent, and oxidation of the surface by coronadischarge, treatment by chromic acid, treatment by flame, treatment byheated air, or irradiation by ultraviolet light in the presence ofozone.

For plastic substrates, an organosilane primer layer may be used toenhance the bonding between the (e.g. coated) substrate and theantiglare surface layer. Generally, an organosilane primer layercontains a very high concentration of hydroxyl groups and high angleSi—O—Si bonds. These are the bonding sites for the antiglare surfacelayer. Permanent bonding is formed by condensation reactions between theantiglare coating composition and the organosilane primer layer. TheSi—O—Si bonds are extremely durable.

For glass substrates, a silicon oxide layer is preferably disposedbetween the substrate and the antiglare layer. Such silicon oxide layeris surmised to improve adhesion of the antiglare layer to the substrate.Further, the presence of the silicon oxide layer can also improve thedurability of the antiglare layer and thus the article. For example adisplay article having such a silicon oxide layer present can exhibit atleast a 25% increase in scratch resistance as determined by theNanoscratch Test. For example, scratch resistances of at least 20 mN, atleast 30 mN, or at least 40 MN have been obtained. The silicon oxidelayer may be applied by various methods, including sputtering,evaporation, chemical vapor depositions and sol-gel methods. U.S. Pat.Nos. 5,935,716; 6,106,892 and 6,248,397 disclose deposition of siliconoxide on glass.

After coating the antiglare coating composition, the coated substrate isthermally cured to drive off solvents and form a dense three-dimensionalfilm structure by thermally inducing self-condensation reactions withinthe coating material, which remove hydroxide groups from the remainingsilanol molecules and bond the structure together with the underlyingsubstrate. This can be accomplished in a batch process within anelectrical resistance element or gas fired oven with total cycle timesranging from 1.5 to 3 hours duration. Durability is generally enhancedas a result of full densification. Although complete densification ofthe coating composition typically occurs at about 800° C., the curingtemperature is chosen based on the heat resistance of the substrate.

A preferred method of curing an organosilane solution, particularly whenapplied to doped tin oxide coated glass, is described in U.S. Pat. No.6,406,758, incorporated herein by reference. Such method involves acombination of heat and infrared radiation in a chamber equipped withinfrared lamps or externally wound heater tubes emitting infraredradiation in the 2.5-6.0 micrometer wavelength spectrum. The use ofinfrared radiation introduces more energy into the coating while at thesame time reducing the thermal exposure of the glass substrate. In doingso, the curing temperature can be reduced to less than about 550° C.

The thickness of the cured antiglare land layer (i.e. at the locationsof the unstructured land) is typically at least 0. 5 micrometers.Further the thickness of the antiglare land layer is typically notgreater than 1.5 micrometers.

The antiglare layer may further comprise an antimicrobial layer disposedon the surface. A suitable antimicrobial layer is a liquid crystalsilane having the general formula:X₃Si(CH₂)_(p)Z  (Formula II)

-   wherein p>1;    X is selected from the group Cl, Br, alkoxy, hydroxyl radicals, and    mixtures thereof, that are hydrolyzable to form a silanol; and

Z is a functional group selected from the group alkyl quaternaryammonium salts, alkyl sulfonium salts, alkyl phosphonium salts,substituted biphenyls, terphenyls, azoxybenzenes, cinnamates, pyridines,benzoates, and mixtures thereof Such liquid crystal silanes arecommercially available from Dow Coming, Midland, Mich., under the tradedesignations “Dow Corning 5700” and “Dow Coming 5772”. Suchantimicrobial layers can provide additional scratch resistance.

Glare reducing transparent substrates (e.g. glass) are utilized in awide array of applications such as cathode ray tube screens or otherdisplay devices (monitors, televisions, liquid crystal displays, etc.);input or selection devices such as touch screens or input panels; glassenclosed displays (museums or other public displays); optical filters;picture frames; windows for architectural applications; glass componentsemployed in mirrors; solar collector cover plates; optical lensesutilized in eyewear and viewing devices; and windshields for vehicles.

Advantages of the invention are further illustrated by the followingexamples, but the particular materials and amounts thereof recited inthe examples, as well as other conditions and details, should not beconstrued to unduly limit the invention. All percentages and ratiosherein are by weight unless otherwise specified.

EXAMPLES

Test Methods

Polishing Wear Test

Coated glass was cut to 3 cm×4 cm rectangular samples. Edges and cornerswere sanded to minimize breakage. The samples were then washedthoroughly with water to remove particulate, then with isopropanol-basedglass cleaner, and then soaked in acetone for 1 minute in order toremove residual water. The samples were then wiped clean using alint-free cloth, allowed to air dry for 30 minutes, and then weighed(Mettler Toledo International Inc., Columbus, Ohio, P.N. AX205).

The samples were polished on the coated side of the glass for 30 minutesat 100% amplitude in 180 g sample holders. The polishing instrument wasa Buehler VIBROMET 2 Polisher (Buehler LTD, Lake Bluff, Ill., P.N.67-1635). The polishing cloth was Buehler Microcloth (Buehler LTD, LakeBluff, Ill., P.N. 40-7222). The polishing media was a slurry of 50 g of1.0 micrometer alumina powder in 1000 ml of deionized water (MICROPOLISHII, Buehler LTD, Lake Bluff, Ill., P.N. 40-6321-080). After 30 minutesof polishing at 100% amplitude, the samples were removed, washed inwater, then isopropanol-based cleaner, and then acetone. The sampleswere then wiped with a lint-free cloth, air-dried for 30 minutes, andthen reweighed.

After 120 minutes of polishing, the samples were left to polish untilcontinuity could be made between two points at the surface. Using amultimeter, resistance was measured at two points 2 cm apart in thecenter of each coated glass sample.

Wear rate was calculated as the total weight lost over the course of 120minutes of polishing time. Time to failure was the time at whichcontinuity was made between two points 2 cm apart.

Nanoscratch

Nanoscratch resistance was measured using a Nanoscratch tester (CSMInstruments, Needham, Mass.). Testing was performed using a progressivescratch load increasing from 2 mN to 100 mN. A 2-micrometer sphericaldiamond indenter was used as the probe.

Abrasion Resistance

A Taber Abraser 5130 (Taber Industries, North Tonawanda, N.Y.,) was usedto abrade the samples. Two CS-10F abrasive wheels (Taber Industries,North Tonawanda, N.Y.) were used that consist of Al₂O₃ particlesembedded in rubber. Each wheel was weighted with 500 g and resurfacedwith 150 grit sandpaper (Taber Industries, North Tonawanda, N.Y., P.N.ST-11). Abrasion was conducted for 100 cycles on the samples with thewheels being resurfaced for another 25 cycles on the sandpaper.Resistance was measured between the printed center point and surroundingring before abrasion and after each set of 100 cycles.

Glass was printed with a thick film of silver paste in a test patternconsisting of two concentric rings surrounding the wear region createdby the Abraser. The glass samples were then coated, fired, and cut into5 inch (12.5 cm) squares. Failure is defined as a 25% increase inelectrical resistance.

Transmission

The transmittance of the article was measured using a BYK GardnerHaze-Guard plus.

Transmitted Haze

The transmitted haze of the article was measured using a BYK GardnerHaze-Guard plus.

Clarity

Clarity of the optical articles was measured using a BYK GardnerHaze-Guard plus. The sample was positioned perpendicularly to the lightsource path. Clarity is calculated from the values of unscatteredtransmitted light and light scattered less than 2.5° from the incidentbeam, as measured by circle and ring photo detectors.

Reflected Haze

Reflected haze was measured with a BYK-Gardner Haze-Gloss Meter.

Reflectance

Reflectance was measured using a BYK-Gardner TCS II at 550 nm withspecular reflection included.

Example 1

A 3 kg batch of an antiglare coating composition was prepared asfollows: In a vessel equipped with a stirring paddle, 31.55 weight %tetraethoxysilane (Dynasil A, Sivento Corp.) was added to 17.99%methyltriethoxysilane (Dynasilan MTES, Sivento Corp.). Stirring was thenstarted and continued throughout the mixing process. 0.53% DP5540(Nyacol Corp) (30% 100 nm colloidal silica dispersed in ethylene glycol)was then added to the stirring mixture. After 10 minutes, a mixture of9.67% 0.15M hydrochloric acid and 0.15% sodium acetate trihydrate wasadded to the above. After a 2 ½ hour reaction time, alcohol diluentswere added. First, 20.06% 1-butanol, ACS, then, after 10 minutes, 20.05%of 2-propanol was added. The completed coating composition was keptstored under constant stirring. Before use, the coating composition wasaged for 2½ days in a closed container at room temperature underconstant stirring. The coating composition was then gravity filteredthrough a 25 μm mesh filter prior to coating.

Example 1 was coated onto two different substrates. The first substratewas soda lime glass. The second substrate was a display panel for atouch screen that was comprised of clean, soda lime glass plates with afluorine-doped tin oxide transparent conductive coating disposed on oneside a thin (i.e. less than 25 angstroms) layer of silicon oxidedisposed on the conductive coating, and a thick film circuit, asdescribed in U.S. Pat. No. 6,727,895, further disposed upon the siliconoxide layer. During heating the thick film circuit penetrates thesilicon oxide layer such that electrical contact is made with theunderlying conductive layer.

The coating was applied to either the glass or the silicon oxide layerof the display panel with a precision dip coating machine at awithdrawal speed set at 0.13 inches (0.33 cm) per second. A suitableprecision dip coating machine is available from Chemat Technology,Northridge Inc, Calif. under the trade designation “Dip-Master 200”.After the dip coating cycle was complete, a one-minute drying time wasallowed to elapse before the coated substrates were removed from the dipcoating machine enclosure. The coated substrates were then cured in aninfrared curing oven as disclosed in U.S. Pat. No. 6,406,758.

An anti-scratch and anti-microbial treatment was then applied to thecoated substrates by applying a homeotropic liquid crystal silanesolution to the substrates and curing as disclosed in U.S. Pat. Nos.6,504,582 and 6,504,583. Although the exemplified construction includedsuch liquid silane surface layer, similar results were obtained withoutthis layer (i.e. antiglare layer present on the surface).

The antiglare surface layer was viewed with a microscope at amagnification of 50× and 20×. The 50× magnification of the antiglaresurface layer of Example 1 is depicted in FIG. 5, whereas the 20×magnification is depicted in FIG. 6. It was also confirmed by opticalmicroscopy that the surface structures were composed of discrete silicaparticles and are therefore true aggregates.

The surface area fraction of the surface structures was determined to be31% for Example 1 as determined using optical microscopy and imageanalysis Software (Image Pro Plus 4, Media Cybernetics).

The optical properties of the coated substrates in comparison to acontrol lacking the antiglare layer were evaluated. Table 1 as followsreports the average value for at least 3 samples and the standarddeviation:

TABLE 1 Reflectance Coating Composition Transmission at 550 nm Reflected(Substrate) (%) Haze Clarity (%) Haze Control - glass with 86.5 ± 0.5%0.5 ± 0.1% 100% 11.4 ± 0.5  37 ± 3% transparent conductive coatings butno antiglare coating Example 1 (glass) 91.5 ± 0.5   5 ± 1 85 ± 3  7.0 ±0.5 470 ± 30

The durability properties of the coated substrates were evaluated. Table2 as follows reports the average value for at least 3 samples and thestandard deviation:

TABLE 2 Polishing Coating Wear Test Nano Scratch Nano ScratchComposition Time to Failure (through top layer (through top layer and(Substrate) (min) only) silicon oxide layer Example 1 255 ± 16 45 ± 5 mN60± mN glass with transparent conductive coating

1. A coating composition comprising an organosilane, colloidal silicaparticles having a mean particle size ranging from 0.05 micrometers to0.15 micrometers, and flocculated silica particles ranging in size fromgreater than 2 micrometers to 100 micrometers.
 2. The coatingcomposition of claim 1 wherein the coating composition comprisesflocculated and colloidal silica particles at a concentration of lessthan 10 wt-% of the coating composition.
 3. The coating composition ofclaim 1 wherein the coating composition comprises flocculated andcolloidal silica particles at a concentration of less than 5 wt-% of thecoating composition.
 4. The coating composition of claim 1 wherein thecoating composition comprises flocculated and colloidal silica particlesat a concentration of less than 2 wt-% of the coating composition. 5.The coating composition of claim 1 wherein the coating compositioncomprises flocculated and colloidal silica particles at a concentrationof less than 1 wt-% of the coating composition.
 6. The coatingcomposition of claim 1 wherein the coating composition comprisesflocculated and colloidal silica particles at a concentration of lessthan 0.5 wt-% of the coating composition.
 7. The coating composition ofclaim 1 wherein the organosilane comprises silicon alkoxides.
 8. Thecoating composition of claim 7 wherein the silicon alkoxides areselected from tetraethoxysilane, methyltriethoxysilane, and mixturesthereof.
 9. The coating composition of claim 1 wherein the coatingcomposition is an alcohol-containing coating composition.
 10. Thecoating composition of claim 1 wherein a least a portion of theflocculated particles have a particle size greater than 10 microns. 11.The coating composition of claim 1 wherein a least a portion of theflocculated particles have a particle size greater than 20 microns. 12.A coating composition comprising an organosilane, colloidal silicaparticles having a mean particle size ranging from 0.05 micrometers to0.15 micrometers, and flocculated silica particles ranging in size fromgreater than 2 micrometers to 100 micrometers; wherein the coatingcomposition has a transmission of at least 90% and is suitable forreducing glare.
 13. The coating composition of claim 12 wherein a leasta portion of the flocculated particles have a particle size greater than10 microns.
 14. The coating composition of claim 12 wherein a least aportion of the flocculated particles have a particle size greater than20 microns.